158 
NAUTILOIDEA. 
Again, in 1881 Sir William Dawson^ described a new species of 
Piloceras (P. amplum) from the Calciferous Sandstone of Lachute, 
near Montreal, which threw much new light upon the internal 
structure of the shell. 
But the most complete examples of Piloceras hitherto met with 
were collected in 1885 by Messrs. Seeley and Brainerd, at Fort 
Cassin, in the State of Yermont, from rocks considered to be of the 
age of the Birdseye Limestone ( = the Lower Llandeilo, nearly). 
These fossils were described and beautifully illustrated by Professor 
E. P. Whitfield, of New York ^ who was enabled to show, by means 
of almost perfect specimens, the body-chamber, septa, siphuncle 
(in place), and even the test of the species, which he very appro- 
priately named Piloceras explanator. 
M. Barrande whose information about Piloceras was very scanty, 
constituted it a subgenus of Cijrtoceras, on account of its curvature ; 
and Professor Blake ^ disposes of it in the same way, though only 
provisionally, for he remarks, “ The organism, whatever it is, must 
wait further elucidation by materials not yet extracted from the 
rocks.” 
Finally, in 1883, Mr. B. N. Peach, of the Geological Survey of 
Scotland, found specimens of Piloceras at the typical locality, Dur- 
ness, Sutherlandshire, in which both septa and siphuncle were 
preserved, though in a very imperfect condition. 
In comparing the structure of Piloceras with that of other 
Cephalopods, we are at once reminded of Endoceras, and the 
resemblance between these two forms did not escape Salter’s ex- 
perienced eye. In both genera the siphuncle is very large in 
proportion to the shell, and in both it is furnished with a series of 
conical or funnel-shaped sheaths, communicating with one another 
by means of an endosiphon. 
Professor Hyatt, whose conclusions regarding the present genus 
are based upon Principal Dawson’s paper, explains the origin of the 
sheaths in Piloceras to be due to the widening of what he terms the 
“ fleshy siphuncle ” near the body-chamber. The sheaths lie some- 
what loosely in the siphuncle, and they are supposed bj^ Dawson, 
upon the evidence of the specimen described by him (fig. 18), to 
have existed only temporarily, and to have been successively 
absorbed, the last one only becoming completely calcified. In the 
^ Canadian Naturalist, new ser. voL x. no. 1. 
^ Bull. Anier. Mus. Nat. Hist. vol. i. no. 8, p. 323, pi. xxyiii. (New York, 1886). 
3 Syst. Sil. de la Boheme, vol. ii. Texte, v. 1877, p. 905. 
British Foss. Cephalopoda, pt. i. p. 186. 
